Restriction on sending mails to some Groups!

Hi All!
   I am having around 50 notes client who are using some groups address for sending mails. These groups are at the server's address book. Now I want to restrict some user to send mails at some of the groups addresses. I want some way so that in less effort I can assign these restrictions at some central place and may edit on requirement. How can I achieve this?

Adding more to this question:

If I made restriction on the name of the group then a user can copy the group on his local machine and rename it. In such a case that restriction will be of no use.
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